A typical liquid crystal display is composed of a plurality of data lines D1, D2 . . . Dy and a plurality of scan lines G1, G2, . . . , Gx. The data lines cross the scan lines. Each pair of data lines and scan line controls a pixel unit. For example, the data line D1 and the scan line G1 controls a pixel unit 100.
FIG. 1 illustrates an equivalent circuit of pixel unit 100. Each pixel unit includes a thin film transistor 101, a storage capacitor Cs and a liquid crystal capacitor Clc that is composed of a pixel electrode and a common electrode. The gate electrode of the thin film transistor 101 is connected to the scan line G1. The drain electrode of the thin film transistor 101 is connected to the data line D1. The scan signal in the scan line may turn on the thin film transistor. Then, the image signal in the data line D1 is transferred to the pixel unit 100.
Scan line drive circuit 102 may send a scan signal to the scan lines G1, G2, . . . , Gx. When one of the scan lines is selected by the scan signal, the thin film transistors connected to this scan line are turned on and the thin film transistors not connected to this scan line are remain turned off. At this time, data line drive circuit 104 may send out an image signal to the data lines D1, D2 . . . Dy to display a corresponding image. After all scan lines are driven by the scan line drive circuit 102, an image frame is displayed.
However, the scan signal is transferred through a long scan line, which delays the scan signal. FIG. 2 illustrates the scan signal delay phenomenon. In an example, the scan line G1 is used to describe the delay phenomenon. The waveform of the scan signal on the starting side of the scan line G1 is the waveform 201. When the scan signal is transferred to the remote end of the scan line G1, the waveform of the scan signal is changed to the waveform 202. Comparing the waveform 201 with the waveform 202, a serious delay phenomenon happens in the rising stage and in the falling stage. Such delay phenomenon delays the turning on the transistor connected to the remote end of the scan line G1. Therefore, the time of the transistor connected to the starting side is in an “ON” state for longer period of time than the transistor connected to the remote end. Such a time difference may shorten charging time of the storage capacitor in the remote end of the scan line. The scan signal delay phenomenon may also cause the transistors respectively connected to adjacent scan line to be turned on together.
Typically, a trigger signal 301 is used to resolve the foregoing problem as shown in the FIG. 3. The trigger signal 301 forms a time interval t between two scan signals. For example, period 302 is the period of the scan line G1. Period 303 is the period of the scan line G2. A time interval t exists between the two periods 302 and 303. The cut-off point of the thin film transistor is the point 306. Accordingly, the waveform of the scan signal in the starting side of the scan line G1 is the waveform 304. The waveform of the scan signal in the remote end of the scan line G1 is the waveform 305. Although a delay phenomenon occurs between the waveform 304 and waveform 305, the case of the transistors respectively connected to adjacent scan line being turned on together may be avoided because of the interval t. That is that after the scan line G1 is scanned, a time interval t passes before the scan line G2 is scanned. Therefore, a data 307 can be completely written into a corresponding storage capacitor.
Although a time interval t may be used to resolve the foregoing problem, the time interval has to be lengthened to ensure the storage capacitor in the remote end of a scan line is completely charged. The lengthened time interval may affect the display quality.